Plural-ply paper and method of manufacture with one or more conductive plies



H. R. PLURAL-PLY PAPER AND Aug. 7, 1962 DALTON 3,048,515 METHOD oF MANUFACTURE WIT ONE 0R MORE coNDUTIvE PLIEs Filed Jan. 11, 1960 -iin mm mm m nm mv.

T .uw N \\N A- H Ilm lllllll -D F Patented Aug. '7, 1962 York Filed Jan. 11, 19,60, Ser. No. 1,681 14 Claims. (Cl. 162-126) This invention relates to the art of paper making and more especially it relates to the making of paper sheets having differential electric conductivity through at least a part of the paper thickness.

A principal object of the invention relates to the making of paper wherein the back of the paper is white or light colored in itself, and the frontside of the paper is dark or black, the portion of the paper adjacent the front side having precisely controlled electric conductivity.

Another object is to provide a method of making paper suitable for use in electric recorders, especially those of the electrically energized recording stylus kind, wherein the nonrecording surface of the sheet, ordinarily referred to as the back of the sheet, is of whitish hue and the front of the sheet has strata of precisely controlled electric conductivity. Y

A -feature of the invention relates to a novel recording paper blank which has, in the brous body thereof, as distinguished from coatings on 'the paper, regions through its thickness of respectively 4controlled electric conductivity, whereby the paper has the normal appearance of a white backing `and yet is capable lof producing sharp electric recordings by visual contrast between the recorded areas and the non-recorded areas on the front of the sheet.

Another feature relates to a recording paper which has more accurately controlled electric conductivity characteristics while preserving the white back surface thereof.

Other Ifeatures and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.-

In the drawings:

FIG. l is a schematic diagram of a system of apparatus for making one embodiment of the paper according to the invention;

FIG. 2 is a perspective view of a section of one of y the papers `according t-o the invention;

FIG. 3 is a modification of FIG. 2 having a separate conductive coating applied thereto;

FG. 4 represents a modification of the paper of FiG. 2; i

FIG. 5 shows the paper of FIG. 4 with a mask coating applied thereto.

In the electric recording art, numerous forms of recording papers have been proposed and used heretofore, including so-called electrosensitive papers. The present invention is in the nature of an improvement on the kind of paper disclosed in U.S. Patents No. 2,398,779 and No. 2,664,044. In general, such a paper consisted heretofore of a White or light-colored paper stock which, of course, in itself is a non-conductor. In order to achieve the required electrosensitive response for electro-recording, it has been the practice to apply one or more coatings of electrically conductive material to the normally white paper.

The coating material that has been found satisfactory hereltofore consisted in general of a mixture of powdered electrically conductive carbon with a suitable binder. Typical of such coatings are -those referred to in said U.S. Patents No. 2,398,779 and 2,664,044. Such papers required, in addition to the paper makingmachines, special coating mixtures, and special coating machines to insure that the several coatings are applied in just the right thickness, uniformity, and controlled electric conductivity. The manufacture of such papers, therefore, required extensive-capit-al investment in the paper making machinery thickness.

and the precision coating machinery. Furthermore, since the electrosensitiveness is dependent upon the coatings, there is always the possibility that the coating mechanism may become out of adjustment and may produce irregular or even minutely striated lines in the coating, which `although not visible to the naked eye, may detract from the desirable surface uniform conductivity. Since such papers are usually recorded on by means of a recording stylus or by a point ldischarge recording electrode arrangement, the uniform electrosensitiveness of the coating must be the highest obtainable over the entire area of the blank. As disciosed in said patents, in order to render the recorded areas visible, it may be required that the paper be provided on its front face With an extremely thin masking coating of a white or light colored hue, which masking coating is physically removed by the recording currents. This removal at the recorded `areas exposes the black or dark hue of the undercoating so as Yto produce the desired readable contrast between the recorded areas and the nonrecorded areas. It is highly desirable, therefore, that during such recording only the said masking coating be removed. However, ysince the said masking coating is of extreme thinness and usually of such a thinness that it cannot lbe accurately measured by ordinary measuring instruments, and may be as thin as 0.0001 inch, there is always the likelihood that the recording current in removing the masking coating will eat into or remove some or all of `the underlying conductive layer which had been .applied as :a separate coating as distinguished from the .the contrast at the recorded areas because the White hue of the back surfaceof the paper may be seen through such thinned outareas. Also it may change the otherwise uniform conductivity of the said lconductive coating, which in effect changes the overall conductivity characteristics of -the blank from those possessed in the absence of record- The present invention overcomes all the above noted objections, in that, instead of using a carbon-containing coating to impart the desired electric conductivity to the blank, the conductivity is imparted during one stage of the actual manufacture of the paper so that the conductivity does not depend upon conductive coatings, and yet the paper, considered as a Whole, has its back surface of white hue and the remaining thickness of the paper adjacent the front surface is of black or dark hue. Such a paper, therefore, avoids the difficulty of the prior conductive coatings being accidentally removed by scratching or wear. The net result is that the finished paper has the normal White appearance on its back surface and it contains Within itself adjacent the front surface, which is acted upon by a recording electrode, the desired conductivity. lf desired, the black conductive surface of the paper proper can be provided with an additional coating of conductive carbon with a binder to form a coatin(r which is of higher resistance than the black portion of the paper proper, thus imparting to the blank a graded or stepped conductivity through its Preferably, however, and in accordance with one aspect of the invention, the paper proper can be made so that in itself it has plies of different electric conductivity.` Thus, `the paper can be made in a plurality of separate passes. For example, the first pass which is formed from paper pulp containing a precisely controlled amount of electrically conductive powder such as powdered carbon or graphite; the third pass which forms the third ply is also formed from a paper pulp containing a precisely controlled amount of electrically conductive powder such as carbon or graphite, but with the amount of conductive powder in the third pass different from and preferably less than that in the second pass.

Referring to FIG. l, there is shown one typical organization or system of apparatus for making the papers according to the invention. Since paper making machinery is well known in the art, only those parts of such machinery as are required to understand the invention are schematically shown in FIG. l. For a more detailed description of such machinery, reference may be had to the book entitled The Manufacture of Pulp and Paper, published by McGraw-Hill Book Company, 2nd edition, 1929, volume V, Section 1, Part 5, particularly at pages 251-282. Accordingly in FIG. l, the numeral represents the vat containing any well known pulp slurry 11, the pulp having been beaten by any well known pulp beater mechanism. The slurry may be that used in any paper manufacturing process, such for example as ground wood pulp, sulte pulp, soda pulp, etc., or a combination of such known pulps either bleached or unbleached. Preferably the pulp 11 is of a bleached or white hue although, if desired, any suitable coloring agent may be added to the pulp in the beater stage for example. In the well known manner the liquid or semi-liquid pulp slurry. 11 is transferred by the mold roller 12 and couch roller 13, on to the well known traveling lower felt 14, which thereafter passes through another pulping unit 15 which may be similar to unit 10. However, the pulp slurry 16 in unit 15, in addition to having the usual paper pulp material, has mixed therewith in any suitable beater a precisely determined quantity of conductive powdered material such as carbon or graphite. The carbon serves the double purpose of imparting a dark or black hue to the slurry 16 and also imparting the desired electric conductivity thereto.

The conductive slurry 16 is applied over the previously formed white non-conductive pulp layer from slurry 11 with which it mates, but Without materially affecting .the previously formed white slurry layer on the felt 14.

These two mated layers, one of which is of whitsh hueA and the other black, are therefore electrically distinct but physically mated or unitized on the felt 14. The mated layers, after leaving vat 15, are carried by the lower felt 14 around the usual strain roll 17 and into contact with the endless upper felt 18. The felts and the two mated paper pulps pass between a series of rolls 19-22 to abstract the liquid contents of the mated pulps. 'Ihe mated pulps then emerge from the rolls 22 where they are separated from the felts, and they then proceed between the usual press rolls 23 to press the two-ply layers into a unitary sheet of the desired density. The twoply sheet then passes around a series of dryer rolls 24 and thence, if desired, to any well known calendering unit y 25. The finished two-ply sheet of paper 26 emerges from the machine and is of the required thinness but with one side of the paper black and conductive, and the other side of the paper of white hue and non-conductive.

FIG. 2 shows in perspective view a section of the finished paper 26. The two mated batches, derived respectively from the slurries 11 and 16 above described, constitute a single thickness two-ply sheet which may have a total thickness of any desired magnitude determined by the pulping consistencies and adjustments on the paper making machinery. One typical thickness for the paper 24 could be about 0.002 inch to about 0.005 inch, with aweight for example of 45 pounds (25 inches by 38 inches-500 sheets), in which case the thickness of the conductive portion, whether formed from a single pass or a multiple pass, may be for example slightly less than 0.005 inch to slightly more than 0.001 inch. In other words, the thickness of the conductive portion,

whether of single or multiple pass formation, can be approximately percent of the total thickness of the paper.

Merely for ease of explanation, the conductive ply and the non-conductive ply of the single thickness sheet are indicated in FIG. 2 by the separate designation numerals 27, 28 with a dotted line therebetween. It will be understood, of course, that this dotted line is merely schematic and is not intended to indicate any physical division bctween the two parts of the sheet thickness except to indicate that one part (part 28) is conductive and of black hue and the other part (part 27) is non-conductive and of white hue. While the invention is not limited to any particular conductivity for the ply 28, it has been found that when the paper is to be used in an electric recorder,

such for example as a traveling pointed stylus recorder which is electrically energized by signals, of which U.S. Patent No. 2,860,180 is typical, the .amount of carbon that is added to the slurry 16 may be such so that the ply 28 of the finished paper has a resistance of approximately 500 to 5000 ohms, as measured for example by means of a pair of electrodes as illustrated in FIG. 2 of U.S. Patent No. 2,664,044.

If it is desired to use the paper 26 to make so-called electrosensitive or facsimile recording blanks, the conductive ply 28, as indicated in FIG. 3, may have applied thereto as by painting, spraying, kning, etc., a coating 29 containing a powdered conductive carbon in a suitable binder. Examples of such conductive coating materials are given in said U.S. patents. Preferably the coating 29 should have a higher resistance than lthe conductive ply 28 so as to control the sharpness of recording.

Preferably, however, instead of using a. coating to impart the desired differential or graded conductivity to the recording blank, the original paper making machinery,VV

as disclosed for example in FIG. l, can be arranged to make the paper itself of three plies rather than of two plies. In other words, in addition to using the two 'vats such as vats 10 .and 15, a third similar vat may succeed the vat 15, and this third vat may contain a smaller amount of powdered carbon than that in vat 15. Thus, the finished three-ply paper as shown in FIG. 4, has a white back 27 which is an insulator; a low resistance black ply 28a; yand another higher resistance black ply 28h. IMerely by way of example, if the amount of carbon added to the second vat 15 is such as to give the ply 28a a resistance of 500 to 5000 ohms, the amount of canbon that is added to the third vat to form ply 28h may be lower in Iamount so that the ply 28h has a high resistance. Thus, when the three-ply paper is measured for` resistance at its surface, as explained in U.S. Patent No. 2,664,044, it may have a `surface resistance of 1000 to 8000 ohms. It will Ibe understood, of course, that the above figures as to resistance are merely typical and in no way limit the invention so rlar as the production of the differential or stepped conductivity is concerned.

The finished paper, whether of two-ply (FIG. 2), twoply plus conductive coating (FIG. 3) or three-ply (FIG. 4), is therefore capable of being used in any electric recording equipment to produce a record by passing an electric current or discharge through the paper 26 at localized areas where the recording is 4to be effected. Preferably when the paper is to ibe used as a Arecording blank 4for facsimile or other similar electrosensitive or .electro-inscribing recorders, the paper is used so that the black or dark colored conductive surface faces the recording stylus or similar `inscribing electrode. 'Ihus the ply 28b (FIG. 4) or the coating 29 (FIG. 3) of the higher resistance is closer Vto the said recording electrode than is the ply 28a (FIG. 4) or the corresponding ply 28 o-f FIG. 3. In other wor-ds, the low resistance ply 28a (FIG.

4) or the low resistance ply 28 (FIG. 3) acts as a com- 'mon ground return for the recording currents acting on recording areas any of the above noted papers can have its black surface provided with an extremely thin masking coating (see FIG. 5) of any white or light hued pigmented material such for example as described in U.S. Patent No. 2,398,779 or No. 2,664,044. yIn any event Vthe thinness of the masking layer 3G should not substantially exceed that necessary merely to mask the black hue of the conductive portion 26 of the duplex paper. Ordinarily such masking coatings are so thin that they cannot be accurately measured with ordinary thickness measuring equipment, the main requirement being that they produce a light hued sunface of minimum thickness so that when the blank is acted upon `by electric currents from a pointed recording `stylus or electrode, the masking coating 30 is removed at the recording areas to reveal the black or dark hue of the lunderlying duplex paper.

One of the advantages of the duplex paper above described over the use of coated papers such as disclosed in U.S. Patent No. 2,664,044 results :from the factl that more contrasting and sharper recorded copies can be obtained. Furthermore, the paper will respond to a greater range of recording currents. Both these advantages result from the fact that the Ibrous conductive ply 28 or layers 28a, 2811 are not destroyed as easily by the recording current used to remove the masking coating 30. Thus the resistance of high conductive ply 28a remains constant. Furthermore, the contrast between the coating 30 and the non-recorded areas of the blank 27 is not reduced since the black low conductivity ply 26 is not burned up or destroyed or thinned -sufliciently to reveal` the white ply 27. In the case of coated white papers, there is always the possibility that the recording currents will remove or thin the conductive coating sufficiently to enable the white hue of the paper to show through the recorded areas.

Various changes and modifications may be made in the disclosed embodiments without departing from the spirit and scope of the invention. [For example, while FIG. 1 shows a typical paper making machine of the successive cylindrical type for forming the successive batches on the tfelt, it will be understood that the combination of a Fourdrinier unit may be used in combination with a succeeding cylinder unit so that one pass, for example the white pass, may be -formed on a Fourdrinier wire and the succeeding pass or passes may be `formed on cylinder paper 'forming units vof known construction. By the expression intimately mated plies, as used herein, is meant that the plies in the iinished paper are intimately bonded throughout their entire contacting areas to form in eiect `a unitized single thickness sheet wherein the unitization of the plies is eiected by mating them when they are in at least -a semi-liquid :form and then dried Kto 'form the single sheet as distinguished from separate sheets which are [bonded by an intervening adhesive.

What is claimed is:

l. The method yof making a duplex paper of precisely controlled transverse conductivity having superposed plies one of which is of non-conductive fibrous composition and the other of which is conductive fibrous composition, which comprises preparing two paper pulp slurries in at least semi-liquid yform one of which includes a predetermined quantity of powdered electrically conductive material to impart a precisely controlled electric conductivity, forming the slurries while in said semi-liquid form into superposed mated passes, and drying the ymated passes to yform a single plural-ply paper sheet having `one of its plies non-conductive and whitish hue on its exposed face and another ply of accurately controlled electric conductivity and of a hue contrasting with that of said exposed face, lboth said plies being'intimately mated to -form a unitized single sheet.

2. The method according to claim l in which the two plies are :formed in successive passes, the yr-st pass being formed from a bleached pulp rst slurry and the second pass being formed from a pulped second slurry which includes powdered conductive carbon to render the second pass of blackish hue whereby the finished paper has the ysaid vnon-conductive portion of whitish hue `on its exposed `face and the remaining conductive portion is of blackish hue.

3. The method according to claim 2 in which the rst slurry has -a coloring ingredient added thereto to produce a color Ifor the rst mentioned ply which. is substantially contrasting in hue with said Iblack conductive ply.

4. The method of making an electrosensitive recording blank which comprises preparing at least two paper pulp slurries, at least one of which includes powdered electrically conductive material to render it electrically conductive and of contrasting color with the next adjacent slurry, forming said slurries into a two-ply paper with one side of whitish hue and insulating and the other side electrically conducting and of contrasting color with the whitish side, the two plies being intimately and uniformly mated over their entire contacting areas but free from any intervening adhesive.

5. The method according to claim 4 in. which the said conductive ply has applied thereto as a separate coating a conductive powdered material with a binder, to impart to said coating a lower conductivity than that of said conductive ply.

6. The method according to claim 4 in which a third pulp slurry is prepared, said third pulp slurry also including powdered electrically conducting material to form a three-ply paper wherein one of the plies constituting the back of the paper is of whitish hue and insulating and the remaining two plies are of respectively different electric conductivity.

7. A paper specially designed vfor recording in response to electric currents acting on the surface thereof in localized arcas, comprising at least two brous paper plies one of which is of whitish hue and `forms the back of the -paper and the other of which is of blackish hue and is electrically conductive, and an electrically conductive coating on the said conductive ply, both said plies being intimately mated over their entire contacting surface without any intervening adhesive.

8. A paper according to claim 7 in which said coating is of higher resistance than the resistance of the said conductive ply.

9. An electro-inscribable recording blank, comprising a plural-ply single paper sheet formed of two intimately mated and bonded paper plies free from intervening adhesive and constituting a single-thickness sheet, said blank having its back surface formed of one ply which is of whitish hue and non-conducting, while its front surface is formed of another ply which is conductive, and a f masking coating applied to the surface of said conductive ply and contrasting in hue therewith.

l0. A plural ply paper comprised of atleast two plies which constitute a single thickness fibrous sheet, wherein one ply contains electrically conductive carbon and another ply is substantially non-conductive and of contrasting color with respect to the carbon-containing ply, the two plies being intimately mated and bonded to form said single thickness sheet without any intervening adhesive.

11. A paper specially designed for recording in response to electric currents acting thereon at localized areas, comprised of successive plies of dried fibrous paper pulp and Y constituting a single-thickness sheet, one -ply constituting the back of the paper and being non-conductive, another ply intimately mated and bonded to the non-conductive ply without any intervening adhesive, said other ply containing a predetermined amount `of conduct-ive powdered carbon to render it conductive.

l2. A paper according to claim ll in which the said one ply is constituted of bleached paper pulp to impart a whitish hue to the paper back, while the other ply constitutes the yfront ofthe paper and is of blackish hue by reason of said carbon.

13. A paper specially designed for recording in response to electric currents acting thereon at localized areas, comprised of successive plies of dried brous paper pulp constituting a single-thickness sheet, one ply constituting the back of the paper and being non-conductive, and at least two additional plies, all said plies being intimately mated and bonded to constitute said single-thickness sheet without any interveningv adhesive, each of said additional plies having therein predetermined amounts of conductive carbon to render said additional plies of respectively different conductivities.

14. A paper according to c laim 13 in which the conductive ply adjacent the non-conductive ply is of greater conductivity than the next adjacent conductive ply.

References Cited in the le of this patent UNITED STATES PATENTS Davenport Aug. 31,

Kline May 21,

Howard p Apr. 15,

Dalton Dec. 29,

FOREIGN PATENTS Great Britain Oct. 30, 

1. THE METHOD OF MAKING A DIPLEX PAPER OF PRECISELY CONTROLLED TRANSVERSE CONDUCTIVITY HAVING SUPERPOSED PLIES ONE OF WHICH IS OF NON-CONDUCTIVE FIBROUS COMPOSITION AND THE OTHER OF WHICH IS CONDUCTIVE FIBROUS COMPOSITION, WHICH COMPRISES PREPARING TWO PAPER PULP SLURRIES IN AT LEAST SEMI-LIQUID FROM ONE OF WHICHINCLUDES A PREDETERMINED QUANTITY OF POWDERED ELECTRICALLY CONDUCTIVE MATERIAL TO IMPART A PRECISELY CONTROLLED ELECTRIC CONDUCTIVITY, FORMING THE SLURRIES WHILE IN SAID SEMI-LIQUID FORM 